Furuno CSH-84 - Manual (Page 86)

11-4
False Echo by Sidelobe
An ultrasonic wave is emitted only in the direction set by the
TILT lever, however there are some emissions outside the main
beam. These are called sidelobes. The energy of the sidelobe is
fairly weak but when the water is comparatively shallow and the
bottom is rocky and hard, strong signals are detected by the
sidelobe. These are represented on the display as a false echo as
shown below.
Mainlobe
Sidelobe
Mainlobe
echo
Sidelobe
echo
The seabed echo
detected by sidelobe
appears at a certain
tilt angle when the
sidelobe points
vertically.
Figure 11-5 Sidelobe echoes
Noise and Interference
Interference from a sonar on another ship appears on the screen
as shown in (A) below. This interference can be suppressed by
changing the CYCLE setting in TVG•TX on the data setting
window. Interference from electrical equipment on board own
ship appears as shown in (B) below. Noise from marine life ap-
pears on the display as shown in (C). Electrical interference and
marine life noise can be suppressed with IR on the SIGNAL
menu in the data setting window.
(A) Interference from
other sonar (B) Electrical
interference (C) Marine life noise
Figure 11-6 Noise and interference